1. Field of the Invention
The present invention relates to a printed inductor that is three-dimensionally formed on an insulating substrate via through holes.
2. Description of the Related Art
In generally known printed inductors, conductor patterns are formed on the same plane of an insulating substrate in a spiral shape or a meandering (serpentine) shape. However, there are disadvantages with such patterns in that the ratio of the conductor patterns occupying the insulating substrate increases, and it is difficult to effectively form these inductors on the limited region of the insulating substrate. Therefore, technologies have been conventionally proposed wherein a three-dimensional printed inductor is formed on the insulating substrate via through holes and the limited region of the insulating substrate is effectively used. An example thereof is disclosed in Patent document 1.
FIG. 7 is a perspective view of a printed inductor according to a conventional example disclosed in the Patent document 1. As shown in FIG. 7, a plurality of mutually independent printed wiring lines 1 is formed on the top and bottom faces of an insulating substrate 10. Further, both ends of respective printed wiring lines 1, which are formed on the top face, forms connecting terminal portions 11a. These printed wiring lines 1 are disposed parallel to each other in a slant direction, respectively. Further, ends of the respective printed wiring lines 1 on both the top and bottom faces are sequentially and continuously connected to each other through a plurality of through holes 12. As a result, the printed inductor 13 is formed in a spiral coil as the insulating substrate 10 is regarded as the center of axis.
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 7-272932 (Page 3, FIG. 3)
According to the aforementioned conventional art shown in FIG. 7, it is possible to form the printed inductor having a relatively large inductance value (L value) on a limited occupied area of the insulating substrate. However, since the printed wiring lines and the through holes are formed in a spiral shape as the insulating substrate is regarded as the center of axis, the printed wiring lines on both the top and bottom faces of the insulating substrate may be easily bonded dielectrically to each other through the insulating material which exists in the center of axis of the insulating substrate. As a result, when a resonance circuit such as a low-pass filter is composed of the printed inductor and the capacitor, it is difficult to raise Q value of the resonance circuit.
Further, in the aforementioned conventional art, in case of raising the inductance of the printed inductor, technologies have been adopted wherein a magnetic substance film is coated on the surface of the insulating substrate so as to cover the printed wiring lines, or the magnetic substance film is formed in the insulating substrate in a sandwich shape. However, it is not possible to sufficiently secure the thickness of the magnetic substance film although any of the aforementioned technologies is used. As a result, it is difficult to obtain a large inductance value.